1. Field of the Invention
The present invention relates to polymeric articles, particularly to ophthalmic lens blanks or wafers and more particularly to a method for protecting ophthalmic lens blanks or wafers, particularly polymer composition ophthalmic lens blanks or wafers by forming a solvent removable protective film thereon. The removable protective film is removable by application of a solvent to which the polymeric article is inert, such as with water or aqueous solutions.
2. State of the Art
Eyeglass lenses were originally manufactured as a single integral body of glass or plastic. The lenses were individually ground or molded to meet the specifications of a particular ophthalmic prescription. This is clearly a labor intensive process that required costly equipment, highly skilled technicians and required a significant amount of time to perform the tasks accurately.
Modem fabrication of ophthalmic lenses can be economically accomplished in a more rapid manner with a laminated lens construction wherein at least two lens wafers are bonded together with a transparent adhesive. Such lens wafers are described, for example, in U.S. Pat. Nos. 5,149,181; 4,846,913; 4,883,548; 4,867,553; 4,857,553; and 4,645,317 and British Patent Application, publication number 2,260,937A.
The laminate construction enables assembly of composite lenses having any of a large number of different combinations of optical corrections from a relatively small stock of prefabricated lens wafers of different configurations. Pairing of different combinations of a front surface lens wafer with a back surface lens wafer can, for example, provide composite lenses having any of a large number of different powers as the power of the lens is the summation of the powers of the two wafers. Such combinations provide for a large majority of all of the prescriptions required for clear vision. Additionally, the front or rear lens elements may have corrections for far-sightedness (a bifocal area) within one of the lenses. The multi-corrective lens may then be formed by combining (e.g., laminating or fusing) the appropriate combinations of blanks.
Notwithstanding the advantages of using lens wafers in the construction of a composite lens, a problem arises with the use of such lens wafers. Specifically, any contaminates such as dust, dirt, fingerprints and moisture found on the wafer surfaces to be glued may become permanently entrapped at the interface of the wafers in the composite lens upon adhesion of the front wafer to the back wafer resulting in defects in the lens, if those contaminants are not removed before lamination. This adds the potential for additional and significant undesirable work in the lamination of the lens blanks from the stored stock of lenses. These defects would reduce the optical quality of the finished lens and can ultimately lead to lens rejection.
To provide a defect-free composite lens, the wafer surfaces to be laminated together (with a transparent adhesive) should be substantially clean of such contaminates. However, since the wafers are invariably handled during composite lens fabrication, it is particularly difficult to avoid contaminants such as fingerprints and dust on the wafer surfaces. These are particularly undesirable on the surfaces that are laminated together as those contaminants would be permanently secured between the lenses and could not be removed after lamination of the lenses. Contaminants on the exterior surfaces of the finished lenses are not as worrisome as they may be cleaned from the lens by normal cleaning procedures after lamination of the at least two lens blank elements.
The ability to maintain a contaminant-free surface is also important if optical coatings such as anti-reflection layers, abrasion resistant layers, tints, polarizing layers, or ophthalmic coatings are to be applied. Again, any surface damage or contamination underneath added layers would be uncorrectable after application of the optical coating.
Previous methods known in the art neither address nor are applicable to this problem. For example, U.S. Pat. Nos. 3,899,315 and 3,899,314 relate to texture control of glass ophthalmic lenses by use of a protective layer which is removed prior to use. A flat glass lens preform is provided with a thin protective layer of a chemically soluble glass fused thereto. In the manufacturing process, the flat preform is subsequently cut and pressed or slumped to the desired ophthalmic shape and the protective layer subsequently removed by dissolving this in a corrosive reagent, thereby exposing the underlying surface which, while smooth, nevertheless needs to be cleaned. The lens is rendered immediately adaptable to ophthalmic use, without further working (grinding, polishing or cleaning) of the surface. This wet process, however, is not suitable for reagent sensitive molded plastic (e.g., polycarbonates or polymethacrylates) lenses. Furthermore, it has been found that the wet process does not provide a sufficiently clean surface on lens wafers required for laminated ophthalmic lenses.
Another approach to removing dust and grease from a polymer surface is disclosed in U.S. Pat. No. 4,199,375 which describes a method for removing dust and grease from phonograph records by applying a polyvinyl alcohol composition which forms a self-supporting film upon drying. When the film is lifted from the record, dust and grease, which are dissolved in the film, are removed. However, this composition, when applied to plastic lenses or lens wafers, forms films that are difficult to remove.
U.S. Pat. No. 5,883,169 describes a self-supporting removable film on the surface of a plastic lens wafer which does not cross-link to the wafer surface. The removable layer provides a method of cleaning the surface of the lens. Additionally, the removable film provides a level of abrasion protection to the underlying surface. The reference also describes a method of cleaning at least one surface of a lens wafer from contaminates which method comprises:
(a) applying a film forming composition onto at least one surface of a lens wafer, said composition comprising:
(I) a film forming unmodified polymer, and
(ii) a compatible solvent;
(b) removing the solvent from said composition to form a self-supporting removable film that coats the surface of the wafer to which it was applied without being cross-linked thereto which film encapsulates therein at least a portion of the contaminates found on the wafer surface prior to application of the composition thereto; and
(c) removing said film from the surface of the wafer. The film removal is shown as being provided because there is no chemical binding, whether covalent or ionic, between the film and the lens wafer so that the film is accordingly peelable.
The temporary protection of polymeric articles, particularly polymeric articles with optical qualities such as ophthalmic lenses formed by the lamination of individual lens blanks, can be effected by the application of polymeric compositions to the surface of the polymer article, the composition being applied as a film or forming a film on a surface of the polymeric article. The individual lens blank is prepared for lamination or coating by application of a selective solvent to the polymeric film, the selective solvent dissolving, dispersing or otherwise removing the polymeric film but neither reacting with or dissolving the composition of the polymeric article. The solvent even may comprise water or aqueous solutions, although C1 to C5 alcohols and alkylene glycol ethers or any blends of these solvents may also be used.